/*
 *
 *  * Copyright (C) 2015 Square, Inc.
 *  *
 *  * Licensed under the Apache License, Version 2.0 (the "License");
 *  * you may not use this file except in compliance with the License.
 *  * You may obtain a copy of the License at
 *  *
 *  *      http://www.apache.org/licenses/LICENSE-2.0
 *  *
 *  * Unless required by applicable law or agreed to in writing, software
 *  * distributed under the License is distributed on an "AS IS" BASIS,
 *  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  * See the License for the specific language governing permissions and
 *  * limitations under the License.
 *
 */
package com.lark.oapi.okhttp.internal.ws;

import com.lark.oapi.okio.*;

import java.io.IOException;
import java.util.Random;

import static com.lark.oapi.okhttp.internal.ws.WebSocketProtocol.*;

/**
 * An <a href="http://tools.ietf.org/html/rfc6455">RFC 6455</a>-compatible WebSocket frame writer.
 *
 * <p>This class is not thread safe.
 */
final class WebSocketWriter {

    final boolean isClient;
    final Random random;

    final BufferedSink sink;
    /**
     * The {@link Buffer} of {@link #sink}. Write to this and then flush/emit {@link #sink}.
     */
    final Buffer sinkBuffer;
    final Buffer buffer = new Buffer();
    final FrameSink frameSink = new FrameSink();
    private final byte[] maskKey;
    private final Buffer.UnsafeCursor maskCursor;
    boolean writerClosed;
    boolean activeWriter;

    WebSocketWriter(boolean isClient, BufferedSink sink, Random random) {
        if (sink == null) {
            throw new NullPointerException("sink == null");
        }
        if (random == null) {
            throw new NullPointerException("random == null");
        }
        this.isClient = isClient;
        this.sink = sink;
        this.sinkBuffer = sink.buffer();
        this.random = random;

        // Masks are only a concern for client writers.
        maskKey = isClient ? new byte[4] : null;
        maskCursor = isClient ? new Buffer.UnsafeCursor() : null;
    }

    /**
     * Send a ping with the supplied {@code payload}.
     */
    void writePing(ByteString payload) throws IOException {
        writeControlFrame(OPCODE_CONTROL_PING, payload);
    }

    /**
     * Send a pong with the supplied {@code payload}.
     */
    void writePong(ByteString payload) throws IOException {
        writeControlFrame(OPCODE_CONTROL_PONG, payload);
    }

    /**
     * Send a close frame with optional code and reason.
     *
     * @param code   Status code as defined by <a href="http://tools.ietf.org/html/rfc6455#section-7.4">Section
     *               7.4 of RFC 6455</a> or {@code 0}.
     * @param reason Reason for shutting down or {@code null}.
     */
    void writeClose(int code, ByteString reason) throws IOException {
        ByteString payload = ByteString.EMPTY;
        if (code != 0 || reason != null) {
            if (code != 0) {
                validateCloseCode(code);
            }
            Buffer buffer = new Buffer();
            buffer.writeShort(code);
            if (reason != null) {
                buffer.write(reason);
            }
            payload = buffer.readByteString();
        }

        try {
            writeControlFrame(OPCODE_CONTROL_CLOSE, payload);
        } finally {
            writerClosed = true;
        }
    }

    private void writeControlFrame(int opcode, ByteString payload) throws IOException {
        if (writerClosed) {
            throw new IOException("closed");
        }

        int length = payload.size();
        if (length > PAYLOAD_BYTE_MAX) {
            throw new IllegalArgumentException(
                    "Payload size must be less than or equal to " + PAYLOAD_BYTE_MAX);
        }

        int b0 = B0_FLAG_FIN | opcode;
        sinkBuffer.writeByte(b0);

        int b1 = length;
        if (isClient) {
            b1 |= B1_FLAG_MASK;
            sinkBuffer.writeByte(b1);

            random.nextBytes(maskKey);
            sinkBuffer.write(maskKey);

            if (length > 0) {
                long payloadStart = sinkBuffer.size();
                sinkBuffer.write(payload);

                sinkBuffer.readAndWriteUnsafe(maskCursor);
                maskCursor.seek(payloadStart);
                toggleMask(maskCursor, maskKey);
                maskCursor.close();
            }
        } else {
            sinkBuffer.writeByte(b1);
            sinkBuffer.write(payload);
        }

        sink.flush();
    }

    /**
     * Stream a message payload as a series of frames. This allows control frames to be interleaved
     * between parts of the message.
     */
    Sink newMessageSink(int formatOpcode, long contentLength) {
        if (activeWriter) {
            throw new IllegalStateException("Another message writer is active. Did you call close()?");
        }
        activeWriter = true;

        // Reset FrameSink state for a new writer.
        frameSink.formatOpcode = formatOpcode;
        frameSink.contentLength = contentLength;
        frameSink.isFirstFrame = true;
        frameSink.closed = false;

        return frameSink;
    }

    void writeMessageFrame(int formatOpcode, long byteCount, boolean isFirstFrame,
                           boolean isFinal) throws IOException {
        if (writerClosed) {
            throw new IOException("closed");
        }

        int b0 = isFirstFrame ? formatOpcode : OPCODE_CONTINUATION;
        if (isFinal) {
            b0 |= B0_FLAG_FIN;
        }
        sinkBuffer.writeByte(b0);

        int b1 = 0;
        if (isClient) {
            b1 |= B1_FLAG_MASK;
        }
        if (byteCount <= PAYLOAD_BYTE_MAX) {
            b1 |= (int) byteCount;
            sinkBuffer.writeByte(b1);
        } else if (byteCount <= PAYLOAD_SHORT_MAX) {
            b1 |= PAYLOAD_SHORT;
            sinkBuffer.writeByte(b1);
            sinkBuffer.writeShort((int) byteCount);
        } else {
            b1 |= PAYLOAD_LONG;
            sinkBuffer.writeByte(b1);
            sinkBuffer.writeLong(byteCount);
        }

        if (isClient) {
            random.nextBytes(maskKey);
            sinkBuffer.write(maskKey);

            if (byteCount > 0) {
                long bufferStart = sinkBuffer.size();
                sinkBuffer.write(buffer, byteCount);

                sinkBuffer.readAndWriteUnsafe(maskCursor);
                maskCursor.seek(bufferStart);
                toggleMask(maskCursor, maskKey);
                maskCursor.close();
            }
        } else {
            sinkBuffer.write(buffer, byteCount);
        }

        sink.emit();
    }

    final class FrameSink implements Sink {

        int formatOpcode;
        long contentLength;
        boolean isFirstFrame;
        boolean closed;

        @Override
        public void write(Buffer source, long byteCount) throws IOException {
            if (closed) {
                throw new IOException("closed");
            }

            buffer.write(source, byteCount);

            // Determine if this is a buffered write which we can defer until close() flushes.
            boolean deferWrite = isFirstFrame
                    && contentLength != -1
                    && buffer.size() > contentLength - 8192 /* segment size */;

            long emitCount = buffer.completeSegmentByteCount();
            if (emitCount > 0 && !deferWrite) {
                writeMessageFrame(formatOpcode, emitCount, isFirstFrame, false /* final */);
                isFirstFrame = false;
            }
        }

        @Override
        public void flush() throws IOException {
            if (closed) {
                throw new IOException("closed");
            }

            writeMessageFrame(formatOpcode, buffer.size(), isFirstFrame, false /* final */);
            isFirstFrame = false;
        }

        @Override
        public Timeout timeout() {
            return sink.timeout();
        }

        @Override
        public void close() throws IOException {
            if (closed) {
                throw new IOException("closed");
            }

            writeMessageFrame(formatOpcode, buffer.size(), isFirstFrame, true /* final */);
            closed = true;
            activeWriter = false;
        }
    }
}
